1. Field of the Invention
The present invention relates to a light emitting diode (LED) package, which can be easily manufactured and has an enhanced light extraction rate such that light extraction efficiency can be enhanced, while being reduced in thickness, and a method of manufacturing the same.
2. Description of the Related Art
In general, LEDs generate minority carriers (electrons and holes) injected by using a p-n junction structure of semiconductor and then recombine them to emit light. That is, when a forward voltage is applied to a semiconductor of a specific element, electrons and holes are recombined through migration in a positive-negative junction. Then, energy level is dropped, thereby emitting light.
Since the LEDs can irradiate high-efficiency light using a low voltage, the LEDs can be used in home appliances, remote controls, electric signs, displays, various automated equipments and the like.
In particular, as information communication devices are reduced in size and are slimmed, various parts of the devices such as resistors, condensers, noise filters and the like are further reduced in size. Recently, the LEDs are produced in the form of surface mount devices (SMDs) to be directly mounted on a printed circuit board (PCB). Accordingly, LED lamps used for display devices are being developed into SMDs. The SMDs can replace conventional lamps, and be used as lighting devices of various colors, a character display unit and an image display unit.
As the LEDs are applied to various fields, high brightness is required in various lamps such as a home lamp, an emergency lamp and the like. Currently, as a result, high power LEDs are widely used.
Hereinafter, conventional LED packages will be described with reference to accompanying drawings.
FIG. 1A is a plan view of a conventional LED package having a hemispheric lens mounted thereon, and FIG. 1B is a cross-sectional view of FIG. 1A. FIG. 2 is a perspective view of a conventional LED package having a flat lens mounted thereon. FIG. 3 is a graph comparatively showing light extraction rates of the conventional LED packages.
As shown in FIGS. 1A and 1B, the conventional LED package having a hemispheric lens mounted thereon includes a circular frame 11, a plurality of LED chips 12 mounted on the inner bottom surface of the circular frame 11, a molding material 13 such as silicon or epoxy resin for protecting the LED chips 12, and a hemispheric lens 14 mounted on the circular frame 11.
In such an encapsulation-type LED package, the hemispheric lens 14 serves as a buffer, which reduces a difference in refractive index between the LED chips 12 having a high refractive index and the air, such that light extraction from the LED chips 12 can be significantly enhanced. When it can be assumed that an LED chip is an approximate point light source, the hemispheric lens 14 guarantees the vertical incidence of light at the interface between the lens 14 and the external air such that reflection can be minimized. Therefore, such a hemispheric lens may be the most ideal structure for light extraction.
However, high-power and high-brightness LED packages used as backlight units (BLU) of middle-sized or large-sized LCDs or flashes of cameras adopt a large-area chip or a multi-chip structure where a plurality of existing LED chips are used. Therefore, the size of a light source increases. Accordingly, when a hemispheric lens has a considerably large diameter, a large-area chip or a multi-chip structure can be assumed as a point light source.
Therefore, such LED packages are not suitable for lighting devices, cameras, or mobile phones which require an ultra-slim structure.
In this case, a LED package using a flat lens 24 shown in FIG. 2, instead of the hemispheric lens, is applied. However, when the flat lens 24 is used, the light extraction rate of the LED package is considerably reduced, compared with when the hemispheric lens is used.
That is, as shown in FIG. 3, when the light extraction rates of an LED package having no lens, the LED package having a flat lens mounted thereon, and the LED package having a hemispheric lens in accordance with a distance from the center of each package to the LED chips are compared, a distance where the light extraction rates of the respective packages are the largest is about 0.84 mm. At this distance, the light extraction rate of the package having no lens is about 25%, the light extraction rate of the package having a flat lens is about 35%, and the light extraction rate of the package having a hemispheric lens is about 53%.
As described above, the package having a hemispheric lens has the largest light extraction rate. However, the height of the LED package inevitably increases as much as the diameter of the hemispheric lens, which means that the package having a hemispheric lens is not suitable for flashes of mobiles phones and the like. When the LED package having a flat lens is used, the size of the LED package is reduced, but a light extraction rate thereof decreases.